Equipment Latest change 2017-10-02
A description of the equipment made for the Chapel.
- Top mount with Hall sensors to measure the behaviour of the pendulum.
- Wire to suspend the bob.
- Bob, aluminium cylinder filled with ca. 6 kg lead.
- Base assembly allowing precise adjustment of the coil set consisting of:
- Zero cross detection coil.
- Drive coil.
- Rim coil.
- Bob Control electronics to detect center and rim passages and to control the drive coil.
- PC program which takes
the data from the Line Sensors and the Bob Control unit and presents it
graphically and logs the data for later study.
- Analysis program to study the logged data.
- Firmware for the BobControl and Power units.
- The story of the broken cable.
With similar equipment at home I've seen a very regular behaviour of the
pendulum and a Foucault precession which very good matches the
calculated value for this lattitude.
The setup has no Charron ring or something equivalent, but obeys the
timing requirement from Schumacher, that is, to give the drive impulse
at a very particular moment in the swinging period.
There is a substantial amount of ellipse, changing periodically in
direction. But it has hardly any effect on the velocity of the Foucault
The Top mount is rigidly mounted to a purlin of the roof, next to the
open stairs. This gave me a height of about 4.5 meters for the length
of the pendulum.
In the Chapel the Top Mount is attached to a raft of the roof at approx. 8.5 m height.
The wire at home is a piano wire of 0.75 mm diameter, in the chapel it is 0.925 mm diameter (gauge 16).
The bob consists of an aluminium cylider filled with lead. A central
rod allows it to be attached to the wire. On the lower end of this rod
sits a magnet which induces electrical signals in the Zero-crossing
coil and in the Rim coil, and it experiences a repelling force when the
Drive Coil is engaged.
The base assembly contains the Coil assembly and the mechanism for precise centering of the coil assembly
Zero cross detection coil
This small coil at the center of the base-assembly detects the passing
of the Bob. When the Bob is approaching the voltage will rise. When the
Bob is nearly overhead the voltage will fall and cross zero at the
moment that the bob is exactly in the center.
The Arduino software detects this center-crossing and starts the timing for a.o. the DriveCoil pulse.
When the time for one half of the swing differs from the time for the
other half, our zero detection coil is not at the center of the
pendulum's swing. This can be corrected with the centering
The driveCoil, when engaged, provides a repelling force on the magnet
in the Bob's lower stem. This will replenish the energy lost by air
friction in each swing.
The rim coil sits at a somewhat large distance from the center.
Detecting the Bob's passages tells us quite precise what the amplitude
of the pendulum is. Based on this information the duration of the drive
pulse is modified to keep the amplitude as constant as possible.
Bob Control Electronics
The electronics for the BobControl unit consists of some operational
amplifiers to condition the signals from the Center- and Rim coils and
the Hall sensors, and to engage the DriveCoil at the proper moment
during the proper time. At the hart of the electronics sits an Arduino
Here you find the zipped code for the Nano.
Look here for the schematics and a detailed description of the
Power supply Electronics
The whole system is supplied from a 24 Volts battery, which is constantly charged by a mains power supply.
This program collects data from the Arduino
processors in the BobControl unit and the Power unit, present some
data graphically and logs all important data to a server in the
network.It also allows to change several parameters of the Pendulum Contol.
The Analisys Program, also written in FPC and Lazarus IDE shows us the behaviour of the pendulum over
somewhat longer time, as it emerges from the
The Arduino firmware for the units Bob Control and Power.